Extending the dynamic range of the determination of copper by adsorption differential pulse stripping method using a principal component artificial neural network

A principal component artificial neural network (PC-ANN) has been applied for the analysis of the voltammogram data of Cu(II) and Cu(II)–PAN complex for extending the dynamic range of the determination of Cu(II) (5–550 μg/l). A three layer back-propagation network (6:5:1) was used with learning rate (r=0.09) and momentum (m=0.9), with sigmoidal transfer function in the hidden layer and one bias node in the input layer. Overall, the application of PC-ANN enables the extension of the dynamic range of the determination of Cu(II) from its narrow linear range (5–50 μg/l) to the high dynamic range (5–550 μg/l).     

Structure of the surface of synthetic titanosilica

X-ray photoelectron spectroscopy (ESCA), high-resolution NMR (on ²⁹Si nuclei), and mass spectrometry have been used to investigate a synthetic titanosilica (TS) containing 28–37% titanium dioxide. It has been found that titanium siloxane bonds can form in synthetic TS, regardless of the fact that silicon-oxygen polyhedra predominate in the surface layer. The presence of titanium ions in the surface layer of TS leads to its significant rearrangement; this reduces significantly the concentration of centers for the strong adsorption of water.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 240–243, March–April, 1986.     

Effect of preparative conditions of a porous surface layer on the hydrogen permeability of palladium/ruthenium alloy membranes

The possibility of producing a porous surface layer on membranes formed from palladium alloys with mercury and lanthanum has been investigated. Membranes with the highest permeability to hdyrogen produced at temperatues in the range 500–550 K with zinc and 560–570 K with copper had maximum surface porosity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1308–1312, June, 1991.     

Vacancy diffusion in Cu Σ = 9 [110] twist grain boundary

Both the formation energy and the diffusive activation energy of a single vacancy migrating in the first four atomic layers intra- and inter-layer near Cu Σ = 9 [110] twist GB have been investigated by using the MAEAM. The formation of the vacancy is favorable on the first layer (1L) near the GB plane and is spontaneous on sites ‘2’–‘5’ especially ‘2’ and ‘4’. The effects of the GB on the intra- as well as inter-layer migration are mainly for 1L–1L as well as for 1L–1L′, 2L–1L and 3L–1L related to the 1L, respectively. Furthermore, the vacancy in 1L is favorable to migrate in 1L (intra-layer) or through GB plane to 1L′, the one in either 2L or 3L is favorable to migrate to 1L. So the vacancy tends to converge to the first layer near the GB plane.     

Determination of Au,Sb, As,Br, Na,K, Cd,Mn and Cl in rice from Vietnam by neutron activation analysis

Gold, antimony, arsenic, bromine, sodium, potassium, cadmium, manganese and chlorine were determined by neutron activation analysis in various rice seed, brand layer and husk from Vietnam. The following concentration values were found: Au 0.05–0.28 ppm, Sb 0.05–1.08 ppm, As 0.08–0.94 ppm, Br 0.82–6.72 ppm, Na 16.71–25, 71 ppm, K 2582–5163 ppm, MN 19.26–33.43 ppm, Cd 0.51–2.42 ppm and Cl 205.20–828.61 ppm in rice seed. These elements were also determined in brand layer and rice husk. Statistically significant differences /t=0.05/ in Au, Sb, Cd contents were detected in rice seed and rice husk, as well as brand layer with rice husk.     

Accumulation and distribution of elements in rice /seed,brand layer,husk/ by neutron activation analysis

Various rice samples /seed, brand layer, husk/ from Vietnam were analyzed for Se, Hg, Cr, Ni, Sc, Rb, Fe, Zn and Co by neutron activation analysis. The concentration values found /seed/ were the following: Se 0.04–0.07 ppm, Hg 0.02–0.07 ppm, Cr 2.13–8.65 ppm, Ni 1.56–4.95 ppm, Sc 0.02–0.06 ppm, Rb 0.84–2.71 ppm, Fe 26.31–96.07 ppm, Zn 10.65–27.39 ppm and Co 0.02–0.15 ppm. The values were reported in ppm /dry weight/. Statistical analysis /t-test, t=0.05/ showed that the content of elements varies between sorts of rice; the content of Rb, Fe, Ni, Cr of rice husk was significantly higher than in rice seed and brand layer.     

The structure of water and methanol adsorbed on silica gel by FT-NIR spectroscopy

The NIR adsorption spectra were analyzed quantitatively on the fundamental, combination and first overtone region of OH vibrations of silanol groups, water and methanol adsorbed on mesoporous silica gels. Adsorbed methanol constitutes first layer of about 3 molecules/um^–2 and second layer, the structure of which is similar to that of bulk methanol liquid. Adsorbed water consists of a first layer of about 3 molecules/nm^–2, the second layer of about 9 molecules/nm^–2 and the third layer has a structure similar to the that of bulk water. The molecular configuration at the interface is discussed.     

Influence of low-intensity electromagnetic field on autooscillations of concentration in belousov-zhabotinskii reaction

A study has been made of the influence of an electromagnetic field (EMGF) with a frequency in the 40–60 GHz range and intensity up to 4–8 mW on autowaves of concentration in the reaction of sodium bromate (0.3 M), malonic acid (0.2 M), sulfuric acid (0.45 M), and Ferroin (0.003 M). It has been found that the action of the EMGF leads to decreases in the wavelength by amounts up to 26%. The experimentally measured temperature gradient created by the EMGF in a thin layer of the reaction mixture is no greater than 0.4°K. The value calculated for the solution temperature rise that is required to create the experimentally observed decrease in wavelength is 5–6° K. It is concluded, therefore, that the observed effect cannot be explained solely by thermal action of the EMGF through heating the reaction mixture.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 704–709, November–December, 1989.     

Electrochemical and spectroelectrochemical properties of manganese reconstituted myoglobin

Electrochemical and spectroelectrochemical properties of manganese(III) reconstituted myoglobin (Mn(III)–Mb) have been investigated. No redox wave of Mn(III)–Mb was observed at a highly hydrophilic indium oxide electrode on which rapid direct electron transfer of native myoglobin took place, suggesting the electron transfer reaction of Mn(III)–Mb at an indium oxide electrode is very slow. The rate constant of the chemical reduction of Mn(III)–Mb with dithionite was ca. 20 times smaller than that of native Mb. Using an optically transparent thin layer electrode (OTTLE) cell and Oxazine-170 perchlorate, 5,9-bis(diethylamino)-10-methyl-benzo[a]phenoxazonium perchlorate, as an electron transfer mediator, the redox potential for the Mn(III) Mn(II)–Mb couple was estimated to be −0.32 V versus Ag AgCl (sat. KCl) at 25°C.     

Formation and decomposition of thin rhodium oxide films

Interaction of O₂ with Rh (poly) and Rh (100) has been studied by Auger Electron Spectroscopy and thermal desorption method at O₂ pressures of 10^–5–10³ Pa and at 400–1600 K. At P(O₂)<10^–5 Pa chemisorption of O₂ occurs, at P(O₂)=10^–5–10^–1 Pa surface oxides are formed, at P(O₂)>1.0 Pa a bulk Rh₂O₃ oxide starts to grow. The growth of rhodium oxide film proceeds via the Cabrera-Mott mechanism. Its decomposition occurs via a mechanism including electron transfer across the oxide film, O₂ desorption from the surface layer and rearrangement of the oxide layer.     

MFTIR spectra of polyethylene synthesized on germanium surfaces

MFTIR spectra of thin layers of polyethylene synthesized on the surfaces of germanium monocrystals in the 700–3000 cm^–1 range have been investigated. The optical constants of the polymer n() and () have been calculated in the range of natural absorption corresponding to the C-H valence vibration bands. Dichroism of the 2848 and 2912 cm^–1 bands disclosed is caused by the orienting influence of the monocrystal surface and in value is comparable with values obtained for monoaxially oriented massive specimens of polyethylene having a high degree of crystallinity. There have been established reversible changes of the relative orientation function of the macromolecule surface layer during heating and cooling of the specimens in the temperature range 293–355 K. This is explained by the nematic state of the polymer in the thin layer, the macromolecules of which are chemically bonded to the surface of the germanium monocrystal.Deceased.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 380–383, May–June, 1988.The authors express their gratitude to K. K. Kalnin'sh for valuable discussion of material in the article and to M. E. Yudovich for his assistance in the calculations.     

Quantitative determination of the alkaloids ofAnabasis aphylla by thin-layer chromatography

Summary A chromatographic method has been developed for the quantitative determination of the alkaloids ofAnabasis aphylla — anabasine, aphylline, lupinine, aphyllidine, and anabasamine — and also pachycarpine in the mixture of reduction products of the high-boiling fraction of alkaloids, in a thin layer of alumina.V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 772–776, November–December, 1976.     

Purification of nerve growth factor from the venom of the Central Asian cobraNaja oxiana

A highly purified electrophoreticaly homogeneous protein with a NGF activity of 10·10⁵ BU/mg of protein have been isolated from the venom of the Central Asian cobra by gel-filtration and ion-exchange chromatography followed by preparative isolectric focusing in a thin layer of Sephadex. It has been shown that the NGF isolated is characterized by a molecular weight in the range of 20–30 kD and a pI value of about 7.0.Institute of Biochemistry, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii. No. 4, pp. 546–551, July–August, 1985.     

Adsorption of Cl? ions on electrodeposited rhodium black layer (rhodized electrode) at low concentrations

The adsorption of Cl^– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl^– ion concentrations (c10^–5 mol dm^–3) in 1 mol dm^–3 H₂SO₄ supporting electrolyte. The specific adsorption of Cl^– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined.     

Mass spectrometric diagnosis of the surface nitriding mechanism in a d.c. glow discharge

Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NH_x(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NH_x(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NH_x with iron lead to the formation of iron nitrides via intermediates such as FeNH_2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed.     

Volume diffusion of I− anions in near surface region of silver

Volume diffusion coefficients of I^– anions in the near surface region of silver have been determined using¹³¹I. The distribution of the labelled ions with depth is determined by acid etching and counting the residual activity. The coefficient of diffusion is determined for surface layers of three different thicknesses over the temperature range 373–823 K. The mechanism proposed assumes the dissociation of Ag⁺I^– in surface layer and the diffusion of I^– into the interstitial free space immediately beneath the surface. This process is found to be accompanied by a small negative entropy change.     

Measurement of neutron emission from a SiO2−D2 system

As a new fact, the neutron emission from the d-d nuclear fusion reaction in a SiO₂–D₂ system has been confirmed as well as that in the Ti–D₂ system. By using a liquid scintillation detector, the neutron emissions from 8 sample materials consisted of SiO₂, in which a small amount of deuterium was adsorbed chemically on the surface layer, were measured in the range of temperature between liquid nitrogen temperature and 400 °C. As a result, it was demonstrated that the neutron-emission reactions take place predominantly on the surface layer of sample material.     

Fabrication and Properties of Doped Porous Polysiloxane Sol-Gel Layers on Optical Fibers

Polysiloxane porous layers doped with TiO- and phenyl-groups were fabricated by the sol-gel method. Starting sols were prepared from alkoxides using catalysis by HCl or HF. Stable SiO-TiO-sols were obtained by using HF. Porous gel layers with thicknesses of 0.3–1.1 m were coated on fiber surfaces or silicon wafers. Layers with the refractive index of 1.38–1.48 were prepared. The fractional porosity of the layers was estimated to be 0.1–0.35. The interactions of the layers with vapor or liquid chlorinated hydrocarbons, alcohols or aromatic hydrocarbons have been studied in immersing experiments by measuring the output light intensity from the fibers. The observed changes of the output intensity could be correlated to changes of the refractive index of the layer caused by the penetration of the tested chemicals into the layer pores.     

Thermal Analysis of Semi-Dilute Hyaluronan Solutions

The freezing and melting of water in semi-dilute (0.5–3.0%) solutions of the polysaccharide hyaluronanhave been investigated by modulated differential scanning calorimetry.High molecular weight hyaluronan inhibited nucleation of ice and significantly depressed thefreezing temperature in a dynamic scan conducted at –3.0°C min^–1. Low molecular weight hyaluronan had a weaker and more variable effect on nucleation. Theeffects on nucleation, especially by the high molecular weight hyaluronan, are attributed tothe influence of a hyaluronan network on the formation of critical ice nuclei.Both high and low molecular weight hyaluronan reduced the melting temperature of ice by 0.4–1.1°C, depending on concentration. The enthalpy change associated with this transitionwas significantly reduced. If all of the enthalpy difference is attributed to the presence of non-freezing water, approximately 3.65 g water/g hyaluronan would be non-freezing. This result appears incompatible with published studies on hyaluronan samples of low water content. An alternative hypothesis and quantitative approach to analysis of the data are suggested. The data are interpreted in terms of a small amount of non-freezing water, and amuch larger boundary layer of water surrounding hyaluronan chains, which has slightly altered thermodynamic properties relative to those of bulk water. The boundary layer water behaves similarly to water trapped in small pores in solid materials and hydrogels.This revised version was published online in November 2005 with corrections to the Cover Date.     

Measurement of the diffusivity of benzene in microporous silica by quasi-elastic neutron scattering and NMR pulsed-field gradient technique

The diffusivity of benzene in a microporous silica powder has been measured by neutron scattering and NMR techniques. The measurements have been performed on un-supported silica but the powder has the same characteristics as the active layer of a real membrane. Self-diffusion coefficients of the order of 10^–10 m²s^–1 are found at 300 K by both techniques so that the model of Knudsen diffusion is not valid for benzene in this microporous material. Due to the presence of small pores, the diffusion of benzene in the membrane-material approaches the diffusion regime usually observed in zeolites. Furthermore, the diffusivity of benzene follows an Arrhenius law with an activation energy of 11 kJ mol^–1.